Coupling process in the preparation of disazo diimides

ABSTRACT

The coupling of a bis-acetoacetylamino compound and a diazotized aminophthalic acid proceeds rapidly to the disazo stage in an aqueous solution of a cyclic ether such as tetrahydrofuran at about room temperature or below, e.g., from about 10°C. to about 25°C., to form the disazo tetracarboxylic acid in very high yields. The corresponding diimide is formed by reacting the tetracarboxylic acid with two molecular proportions of ammonia or a primary amine.

THE INVENTION

This invention relates to compounds which can be represented by the general formula: ##EQU1## wherein A is an aryl or substituted aryl group such as a phenylene, polyphenylene or a condensed ring group and B is a phthalic acid, anhydride, or imide radical having the respective formulae: ##SPC1##

Wherein the X radicals are the same or different halogen, lower alkyl or lower alkoxy radicals, n is an integer from 0 to 2 and R is hydrogen, cycloloweralkyl, hydroxyloweralkyl, phenyl, substituted phenyl, naphthyl and lower aliphatic groups such as lower alkyl and lower alkenyl.

The invention particularly relates to a process for preparing these compounds and more particularly to the step of coupling a bisacetoacetylamino compound with a diazotized aminophthalic acid.

Compounds represented by the general formula above are taught in U.S. Pat. No. 3,256,618. It is also taught therein that the coupling of one mole of a diazotized aminophthalic acid with an N,N'-arylene-bis-acetoacetyl amide leads to a monoazo dyestuff which is readily soluble in an alkaline medium so that reaction with another mole of diazotized aminophthalic acid can easily be performed to obtain a disazo tetracarboxylic acid.

The coupling procedure taught in the patent is not satisfactory, however, for attaining complete conversion to the disazo tetracarboxylic acid, especially when A in Formula I is a halogenated aryl group. In some instances the monoazo diacid constitutes as much as 60 mole percent of the final product when an aqueous ethanol coupling medium is employed as taught in the working examples of the patent. The tinctorial strength and clarity of a colorant consisting of a substantially pure disazo tetra-acid and of colorants derived therefrom are significantly greater than of those containing a mixture of monoazo and disazo compounds.

Now it has been discovered that a substantially quantitative conversion to the disazo tetracarboxylic acid is achieved by a coupling method employing an aqueous medium containing a cyclic ether.

It is a principal object of this invention, therefore, to provide a novel method of coupling a diazotized aminophthalic acid with an N,N'-arylene bis-acetoacetamide.

It is another object of this invention to provide an improved method of preparing a disazo tetracarboxylic acid.

It is a related object of this invention to provide an improved method of preparing a disazo diimide.

It is a further object of this invention to provide a method of preparing disazo diimide colorants having a high tinctorial strength and superior clarity.

It is yet another object of this invention to provide disazo diimide colorants having a high tinctorial strength.

These and other objects are achieved according to this invention by a method comprising the steps of coupling one molecular proportion of a bis-acetoacetamide having the formula: ##EQU2## wherein A is an aromatic hydrocarbylene or substituted aromatic hydrocarbylene radical, with two molecular proportions of a diazotized aminophthalic acid having the formula: ##SPC2##

wherein the X radicals are the same or different halogen, lower alkyl or lower alkoxy radicals, and n is an integer from 0 to 2, in an aqueous medium containing a sufficient amount of a water soluble cyclic ether to bring the reagents into solution, thereby producing a disazo tetracarboxylic acid, and reacting said acid with about two molecular proportions of ammonia or a primary amine. Usually, an amount of cyclic ether equal to from about 40% to about 60% of the total volume of the reaction mixture is sufficient. Preferably, a cyclic ether selected from the class consisting of tetrahydrofuran, tetrahydropyran, dioxane and mixtures thereof constitutes about half of the volume of the reaction mixture.

The coupling reaction can be advantageously effected by the addition of an aqueous suspension of two molecular proportions of the diazotized aminophthalic acid to a suspension of one molecular proportion of the bis-acetoacetamide in a 1:1 by volume mixture of water and the cyclic ether. The reaction proceeds rapidly at about room temperature or below, e.g., from about 10°C. to about 25°C. and subsequent to acidification to a pH of about 1 to 2, filtration and drying, the disazo tetracarboxylic acid is obtained in very high yields.

The aromatic hydrocarbylene radical represented by A in formula II above is exemplified by phenylene, biphenylene, terphenylene and other polyphenylene radicals, a divalent naphthalene radical and other divalent polynuclear aromatic hydrocarbylene radicals. Said radicals will generally have from 6 to about 24, preferably from 6 to about 16, carbon atoms. The substituted aromatic hydrocarbylene radicals represented by A may have halogen, lower alkyl or lower alkoxy substituents on an aromatic hydrocarbon radical such as one of those just mentioned. From 1 to about 6, preferably from 1 to about 2, halogen substituents selected from fluorine, chlorine and bromine may be present. Chlorine is a preferred halogen substituent.

The lower alkyl substituents on the aromatic hydrocarbylene radicals include straight and branched chain groups having up to about 7 carbon atoms, and are exemplified by methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, hexyl and the like. The lower alkoxy substituents similarly include straight and branched chain groups having up to about 7 carbon atoms and these are exemplified by methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, t-butoxy and the like. There may be from 1 to about 6, preferably from 1 to about 2, alkyl or alkoxy substituents.

The halogen, lower alkyl and lower alkoxy radicals may be simultaneous substituents on the substituted aromatic hydrocarbylene radicals represented by A. The 2-chloro-5-methyl phenylene radical is an example of such mixed substitution.

In formula III the halogen substituents represented by X may be fluorine, chlorine, or bromine; chlorine being preferred. The lower alkyl and lower alkoxy radicals represented by X include straight and branched chain groups having up to about 7 carbon atoms and are exemplified by the radicals named above with reference to the like substituents on the divalent aromatic hydrocarylene radical A. When X is a lower alkyl or lower alkoxy radical it is preferred that n be 1 but it is generally preferred that n be zero.

The reaction of the disazo tetracarboxylic acid, or the dianhydride thereof, with ammonia or a primary amine produces a diimide of the type represented by formula I.

When it is desired that the imido nitrogen atoms be unsubstituted the tetra-acid or the dianhydride is reacted with ammonia, e.g., that produced by the decomposition of urea. The amine reactant may be represented by the formula H₂ NR wherein R is hydrogen or a lower alkyl, cyclic lower alkyl, hydroxy-lower alkyl, phenyl, halophenyl, nitrophenyl, phenoxyphenyl, phenylaminophenyl, lower alkylphenyl, lower alkoxyphenyl, lower alkyl/halophenyl, lower alkylaminophenyl, acylaminophenyl or naphthyl radical. Examples of the amine include methylamine, cyclohexylamine, ethanolamine, 2,4-dichloroaniline, nitroaniline, toluidine, anisidine, aminodiphenylamine, N,N'-dimethyl phenylenediamine, 2-methyl-3-chloroaniline, and the like.

The disazo diimides may be prepared economically without isolating intermediates by the following procedure: first, remove the residual water and cyclic ether from the presscake formed in the filtration step of the coupling process by distillation from a suspension of the presscake in trichlorobenzene; second, convert the dried disazo tetracarboxylic acid, without separating it from the trichlorobenzene, to the dianhydride by dehydration with acetic anhydride; third, remove acetic acid and any excess acetic anhydride from the reaction mixture as an azeotrope and then convert directly to the diimide by condensation of the dianhydride with a primary amine or ammonia.

The method of this invention will be better understood from the following examples which are intended to be illustrative only.

EXAMPLE 1 N,N'-(2,5-dichloro-p-phenylene)-bis[2-(2,3-dicarboxyphenylazo)-acetoacetamide]

Twenty-one grams (0.1 mole) of 3-nitrophthalic acid are dissolved in 75 ml. of 13% aqueous sodium hydroxide and the solution adjusted to pH 8.2 with dilute acetic acid. Reduction to 3-aminophthalic acid is accomplished by hydrogenation in a low-pressure reactor at 45 psi over a 4 hour period using 0.1 gram of platinum oxide catalyst. At completion, the catalyst is removed by filtration and the resulting solution of 3-aminophthalic acid is cooled to 0°-5°C. and acidified with 50 mls. of concentrated hydrochloric acid. The amine hydrochloride is diazotized with 6.9 grams of sodium nitrite dissolved in water at 0°-5°C. After approximately 15 minutes, the diazo compound precipitates as a white crystalline material. Excess nitrite is then destroyed with sulfamic acid after a 45 minute stirring period and the suspension (about 100 mls.) is employed directly in the step described below.

To 700 mls. of 1.6% aqueous sodium hydroxide is added 17.25 grams (0.05 mole) of N,N'-(2,5-dichloro-p-phenylene)bisacetoacetamide and 30 grams of sodium acetate. When solution is complete, the coupler compound is precipitated by acidifying to pH 6.0 with 50% acetic acid. Tetrahydrofuran is added to the coupler compound suspension in an amount about equal to the total volume of the suspensions of both the diazo compound and the precipitated coupler. The diazo compound is added to the coupler with vigorous agitation. Coupling is complete within 7 minutes producing a bright yellow material. The sodium salt is converted to the free acid with the addition of dilute hydrochloric acid to pH 1.0. The product is filtered, washed and dried at 70°C. to give a yield of 97% theory. The infrared absorbencies are as follows: λmax. KBr (μ) 2.90 (acid OH); 3.22 (amide NH); 5.79 (acid C=O); 5.87, 5.96 (C=O); 6.60, 6.73 (N=N).

EXAMPLE 2 N,N'-(3,3'-dimethylbiphenylene)-bis[2,3-dicarboxyphenylazo)-acetoacetamide]

Into a 500 ml. pressure bottle are added 75 mls. of water, 8.2 gms. (0.205 mole) of sodium hydroxide, and 21.1 gms. (0.100 mole) of 3-nitrophthalic acid. The pH of the solution is adjusted to 8.8 with dilute acetic acid. After addition of 0.1 gm. of Adam's platinum oxide catalyst, the reduction is carried out on a Parr low-pressure hydrogenation apparatus at 3 atmospheres initial pressure. The absorption of the theoretical amount of hydrogen requires 4-5 hours at room temperature. The solution is filtered to remove the catalyst, cooled to 0°C., and 50 mls. of concentrated hydrochloric acid added to precipitate the amine hydrochloride. The suspension of the amine hydrochloride is agitated at 0°C. to 5°C., a solution of 6.9 gms. of sodium nitrite in 50 mls. of water added, and stirred 45 minutes at 0°C. to 5°C.

A coupling component suspension is prepared from 455 mls. of water, 11.0 gms. of sodium hydroxide, 19.0 gms. of N,N'-(3,3'-dimethylbiphenylene)-bis acetoacetamide, and 30.0 gms. of sodium acetate. The pH of this suspension is adjusted to 5.8 with acetic acid, then placed in a 3 liter beaker equipped with an Eppenbach agitator. Provision is made for introducing the diazotized 3-aminophthalic acid directly under the agitator.

Six hundred mls. of tetrahydrofuran are added to the coupler suspension, the agitator started at medium speed, and the diazonium compound slurry run in at a rate which will keep a very slight excess of the diazonium compound (testing by coupling with R-Salt solution). At the same time tetrahydrofuran is added to maintain a concentration of this solvent at approximately 50%. A brilliant yellow product is formed.

The coupling is complete at room temperature in about 10 minutes, and the slurry is agitated for 15 minutes longer. Sufficient hydrochloric acid is added to liberate the tetracarboxylic acid which is separated by filtration and washed. After drying, a yield of 36.6 gms. is obtained, equivalent to 96.1% of theoretical. The melting point is above 370°C. The infrared absorbencies of the product are as follows: λ max. KBr (μ) 2.94 (acid OH); 3.30 (amide NH); 5.74 (acid C=O); 6.61, 6.71 (N=N).

The products of the coupling processes described in the above examples are used in the following examples to illustrate further the steps of the improved method of preparing a disazo diimide.

EXAMPLE 3 A. N,N'-(2,5-dichloro-p-phenylene)-bis[2-(2,3-dicarboxyphenylazo)-acetoacetamide]dianhydride

To a one liter flask equipped with stirrer, thermometer, reflux condenser and drying tube are added 30 gms. (0.041 mole) of the disazo compound prepared in Example 1, 500 mls. of monochlorobenzene, and 16 gms. (0.156 mole) of acetic anhydride. The mixture is heated to reflux and maintained at this temperature for 24 hours, cooled to room temperature, filtered, and washed with 500 mls. of monochlorobenzene. After drying in a vacuum oven, 26.3 gms. are obtained representing 89% of theory. Chlorine analysis is as shown: Calculated: C₃₀ H₁₈ O₁₀ N₆ Cl₂ ; Cl, 10.25. Found: Cl, 10.55. Infrared absorbencies of the product are as follows: λ max. KBr (μ) 3.26 (amide NH); 5.40 (anhydride C--O--C); 5.63, 5.95 (C=O); 6.60, 6.70 (N=N).

B. N,N'-(2,5-dichloro-p-phenylene)-bis{2-[N-(p-chlorophenyl)-2,3-dicarboximidophenylazo]-acetoacetamide}

To a one liter flask equipped with stirrer, thermometer, reflux condenser and drying tube are added 10 gms. (0.014 mole) of the yellow dianhydride, 7 gms. (0.054 mole) of p-chloroaniline, 50 mls. of trichlorobenzene and 50 mls. of glacial acetic acid. The mixture is refluxed for about 24 hours or until a small sample, filtered and washed with ethanol, produces little or no bleed in boiling 3% aqueous sodium hydroxide. When the reaction is complete the product is filtered, washed with 500 mls. of ethanol and dried in a vacuum oven at 90°C. The product is then extracted with boiling 3% aqueous sodium hydroxide, filtered, washed neutral with water, and then dried at 70°C. The pigment is obtained in almost quantitative yield.

The bright yellow diimide pigment of this example is stable to about 390°C., has good lightfastness and is non-bleeding in solvents such as o-dichlorobenzene, acetone, xylene, and perchloroethylene at their boiling temperatures. Elemental analysis is as shown: Calculated: C₄₂ H₂₂ O₈ N₈ Cl₄ ; C, 55.27; H, 2.85; N, 12.28; Cl, 15.57. Found: C, 55.33; H, 3.35; N, 12.09; Cl, 15.40. Infrared absorbencies of the product are as follows: λmax. KBr (μ) 3.35 (amide NH); 5.62 (imide C--N--C); 5.81, 5.96 (C=O); 6.60, 6.73 (N=N).

EXAMPLE 4 A. N,N'-(3,3'-dimethylbiphenylene)-bis[2-(2,3-dicarboxyphenylazo)-acetoacetamide]dianhydride

To a one liter flask are added 300 mls. of monochlorobenzene, and 15.28 gms. (0.02 mole) of the tetracarboxylic acid of Example 2. Water is removed by azeotropic distillation. Acetic anhydride (100 mls.) is added and the contents of the flask are heated at reflux (129°C.) for 15.5 hours. After filtering, washing with monochlorobenzene, and drying in a vacuum oven, a yield of 13.80 gms. of a brilliant yellow solid is obtained, equivalent to 94.8% of theoretical. The melting point is 362°C. (dec.) The infrared absorbencies of the product are as follows: λmax. KBr (μ) 3.12 (amide NH); 5.40 (anhydride C--O--C); 5.63, 5.95 (C=O); 6.60, 6.70 (N=N).

B. N,N'-(3,3'-dimethylbiphenylene)-bis[2-(2,3-dicarboximidophenylazo)-acetoacetamide]

To 250 mls. of anhydrous o-dichlorobenzene are added 7.28 gms. (0.01 mole) of the dianhydride, and 5.0 gms. of urea. The mixture is heated at 165°C. for four hours when a test of a small sample shows no solubility in boiling 3% sodium hydroxide. The yellow pigment is filtered off, washed with acetone and dried in a vacuum oven. A yield of 8.0 gms. is obtained. The melting point is above 370°C. The pigment shows no bleed when heated in the following solvents at their boiling temperatures: 3% sodium hydroxide, o-dichlorobenzene, perclene, xylene, acetone and methylethyl ketone. Infrared absorbencies are as follows: λmax. KBr (μ) 3.14 (amide NH); 5.64 (imide C--N--C); 5.79, 5.97 (C=O); 6.60, 6.73 (N=N).

The superiority of the coupling method of this invention is shown by the following comparison with the aqueous ethanol method taught in the aforementioned patent.

The yield of an azo acid prepared by coupling a diazotized 3-aminophthalic acid with N,N'-(2,5-dichloro-p-phenylene) bis-acetoacetamide in an aqueous coupling medium containing about 5% by volume ethanol was 83.5% of the theoretical amount of the expected disazo tetracarboxylic acid and contained about 40 mole percent of the disazo tetra-acid and about 60 mole percent of the monoazo diacid. The yield of azo acid prepared from the same reactants in the coupling medium of this invention was 97% of the theoretical amount and the anhydride contained about 88.6 mole percent of the disazo product. The product of the instant invention is tinctorially stronger than that of the prior art method.

A sample of the azo acid prepared by the prior art method and weighing 19 gms. took up an additional 3.6 gms. of diazo phthalic acid when the two reactants were mixed in a coupling medium containing about equal volumes of water and tetrahydrofuran. The tinctorial strength of the product after the second coupling reaction was much improved and approximately equal to that of the disazo tetracarboxylic acid obtained in one step by the method of this invention.

In an attempt to increase the conversion to the tetra-acid and, thereby, the yield of product, an excess (3 mls.) of diazo phthalic acid was mixed with one mole of the bis-acetoacetamide in the aqueous ethanol medium of the prior art. There was no increase in yield over that obtained when the stoichiometric 2 mls. of diazo phthalic acid was used and no improvement in tinctorial strength was noted.

The embodiments of the invention illustrated and described herein are merely illustrative and variations which may differ in detail but not in substance will readily suggest themselves to those skilled in the art of making and using pigments. The scope of the invention is not intended to be defined by the illustrative embodiments but the subject matter which the applicant's regard as their invention is particularly set forth in the following claims. 

I claim:
 1. A method of preparing a disazo tetracarboxylic acid having the formula: ##SPC3##wherein A is aromatic hydrocarbylene or substituted aromatic hydrocarbylene, X is the same or different halogen selected from the class consisting of fluorine, chlorine and bromine, or lower alkyl or lower alkoxy and n is an integer of from 0 to 2, said method comprising the coupling of one molecular proportion of a bis-acetoacetamide having the formula ##EQU3## wherein A is as defined above, with two molecular proportions of a diazotized aminophthalic acid having the formula: ##SPC4## wherein X and n are as defined above, in an aqueous medium containing a sufficient amount of a water soluble cyclic ether to bring the reagents into solution.
 2. The method of claim 1 wherein the cyclic ether is selected from the class consisting of tetrahydrofuran, tetrahydropyran, dioxane, and mixtures thereof.
 3. The method of claim 1 wherein the amount of cyclic ether is from about 40% to about 60% of the total volume of the reaction mixture.
 4. The method of claim 2 wherein the ether is tetrahydrofuran.
 5. The method of claim 1 wherein A is a phenylene.
 6. The method of claim 1 wherein A is a 2,5-dichlorophenylene.
 7. The method of claim 1 wherein n is
 0. 8. In a method of preparing a disazo diimide comprising the steps of coupling one mole of a bis-acetoacetamide having the formula: ##EQU4## wherein A is aromatic hydrocarbylene or substituted aromatic hydrocarbylene, with two moles of a diazotized aminophthalic acid having the formula: ##SPC5##wherein X may be the same or different halogen selected from the class consisting of fluorine, chlorine, and bromine, or lower alkyl, or lower alkoxy and n is an integer from 0 to 2, to produce a disazo tetracarboxylic acid, and reacting said acid or the dianhydride thereof with a primary amine or ammonia, the improvement consisting of coupling the bis-acetoacetamide and diazotized aminophthalic acid in an aqueous medium containing a sufficient amount of a water soluble cyclic ether to bring the coupling reagents into solution.
 9. The improved method of claim 8 wherein the cyclic ether is selected from the class consisting of tetrahydrofuran, tetrahydropyran, dioxane and mixtures thereof.
 10. The improved method of claim 8 wherein the ether is tetrahydrofuran. 